Transparent conductor and device

ABSTRACT

According to one embodiment, a transparent conductor includes a transparent substrate; a metal nanowire layer disposed on the transparent substrate and including a plurality of metal nanowires; a graphene oxide layer covering the metal nanowire layer; and an electrical insulating resin layer disposed in contact with the graphene oxide layer.

CROSS-REFERENCE TO RELATED APPLICATION

This application is based upon and claims the benefit of priority fromJapanese Patent Application No. 2014-042574, filed Mar. 5, 2014 theentire contents of which are incorporated herein by reference.

FIELD

Embodiments described herein relate generally to a transparent conductorand a device that uses the transparent conductor.

BACKGROUND

Conventionally, devices using a transparent conductive film have beendeveloped. Examples of such devices include liquid crystal displaydevices, solar cells, organic EL devices, optical devices such asinorganic light-emitting diodes (inorganic LED), and coordinate panelsreferred to as touch panels. Indium-tin oxide (ITO) films are generallyused as transparent electrodes or transparent wiring in these devices.The transparent wiring usually has a very long total length andtherefore requires flexibility. ITO is, however generally brittle andapt to be cracked by bending or other stress. Cracking of the ITO filmleads to an increase in electrical resistance.

The use of carbon materials (a carbon fiber, a carbon nanotube,graphene, or the like) as a conductive material can significantly reducethe amount of rare metals or the like to be used. In some cases, the useof carbon materials even enables no metals or the like to be used.Carbon materials have high flexibility and large mechanical strength,and in addition, are chemically stable. Although individual molecules ofcarbon materials have comparatively high conductivities, the resistancein intermolecular conduction is high. For this reason, when carbonmaterials are used as a transparent electrode having a large area, theelectrical resistance is higher compared to an ITO film of the samelight transmittance. When carbon materials are used for wiring with along total length, the electrical resistance is much higher than thatwhen a metal conductive material such as copper (Cu) is used.

Since a metal nanomaterial has high conductivity, development forimproving the conductivity of carbon materials by using a composite ofthe carbon materials and metal nanomaterial is underway. However, evenwhen the composite is used, it is difficult to obtain a transparentconductor which has high transparency, is excellent in resistance tobending, peeling, and impurities, and is obtainable at low cost.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1 is a schematic view showing a cross-section of a transparentconductor according to an embodiment;

FIGS. 2A and 2B are schematic views showing the fusing of metalnanowires due to the graphene oxide layers in a transparent conductoraccording to an embodiment;

FIG. 3 is a schematic cross-sectional view of a light-emitting deviceaccording to an embodiment;

FIG. 4 is a schematic cross-sectional view of a light-emitting deviceaccording to another embodiment;

FIG. 5A is a schematic view showing a plane of a coordinate panelaccording to another embodiment;

FIGS. 5B and 5C are schematic plan views of wiring boards of thecoordinate panel shown in FIG. 5A;

FIGS. 6A and 6B are schematic cross-sectional views Of the coordinatepanel shown in FIG. 5A; and

FIGS. 7A and 7B are scanning electron microscope (SEM) images of atransparent conductor of an example.

DETAILED DESCRIPTION

According to one embodiment, a transparent conductor includes atransparent substrate; a metal nanowire layer disposed on thetransparent substrate and including a plurality of metal nanowires; agraphene oxide layer covering the metal nanowire layer; and anelectrical insulating resin layer disposed in contact with the grapheneoxide layer.

Hereinafter, the embodiment will be described with reference to thedrawings.

It is difficult to further enhance transparency and bending resistance,and to further decrease electrical resistance in a light-emitting devicein which an inorganic LED and an acrylic resin layer are arranged on atransparent ITO film. A device is known, in which the device is obtainedby sandwiching an inorganic LED between polyethylene terephthalate (PET)films, wherein the PET films have a layer produced by chemical vapordeposition (CVD) and including graphene and a layer including silvernanowire laminated thereon. Such a device has low transmissivity andrequires high cost. A touch panel using a silver nanowire has poorpeeling resistance. Therefore, in such a touch panel, it is difficult tosecure resistance against impurities, sulfur in particular.

The present inventors found a transparent conductor that is low inelectrical resistance and can be provided at low cost, the transparentconductor having high transparency and being excellent in resistance tobending, peeling, and impurities.

FIG. 1 is a schematic cross-sectional view of a transparent conductor 10according to an embodiment. A metal nanowire layer 12 including anaggregate of metal nanowires 12 a, and a graphene oxide layer 13 areprovided on a transparent substrate 11. The metal nanowire layer 12includes a plurality of metal nanowires 12 a. In the metal nanowirelayer 12, a gap may be produced between adjacent metal nanowires thatare spaced apart from each other. In this gap, the graphene oxide layer13 is in contact with the substrate 11. Furthermore, an electricalinsulating resin layer 14 is arranged in contact with the graphene oxidelayer 13.

In the transparent conductor 10, parts of the plurality of metalnanowires 12 a are in contact with or fused to each other, forming anetwork-like structure, such as a net-like structure or a lattice-likestructure. Thus, a plurality of conductive paths is formed, and aconductive cluster spanning the entire transparent conductor is formed(percolation theory). In order to form the conductive cluster, a certainamount of number density is required of the metal nanowire. In general,a longer metal nanowire is more likely to form the conductive cluster,and a metal nanowire having a larger diameter has a higher conductivity.Since a network-like structure using the metal nanowires is formed assuch, the conductive cluster exhibits high conductivity as a whole,although the amount of metal is small. In addition, the obtained metalnanowire layer 12 is flexible.

Graphene oxide can be manufactured from inexpensive graphite, and thegraphene oxide layer 13 is flexible and transparent. The graphene oxideshave high bonding properties and adhesive properties due to hydrogenbonding. Therefore, the graphene oxide functions to fuse the metalnanowires 12 a to each other, thereby enhancing the conductivity of themetal nanowire layer 12, and at the same time improves thermal stabilityand mechanical stability. With reference to FIGS. 2A and 2B, the fusionof the metal nanowires 12 a caused by the graphene oxide will bedescribed. FIG. 2A is a schematic view of the metal nanowire 12 a andgraphene 13 a in the transparent conductor of the embodiment as viewedfrom above. FIG. 2B is a schematic cross-sectional view. A portion ofthe graphene oxides 13 a is in contact with the substrate 11 and arelabeled as graphene oxides 13 a′. Herein, the metal nanowire 12 a issandwiched between the graphene oxides 13 a and 13 a′. The fusion of themetal nanowires 12 a is caused by a strong bonding force 23 between thegraphene oxides.

Furthermore, the graphene oxide 13 a has various effects. For example,the graphene oxide 13 a is a layered substance, and has an effect ofpreventing the diffusion of impurities from outside. Particularly,although the silver nanowire may be corroded by sulfur and compoundsthereof, the corrosion can be prevented by the effect of the grapheneoxide.

The graphene oxide 13 a itself has insulating properties. However, whenthe graphene oxide is applied with a voltage to pass an electriccurrent, a part of the graphene oxide changes to graphene, and therebyallowing the value of electrical resistance to be decreased. For thisreason, good contact between the graphene oxide layer and an electricelement is obtained. The graphene oxide 13 a can also dissolve a part ofthe metal nanowires 12 a to promote the fusion of the metal nanowires 12a and can precipitate the dissolved metal as nanoparticles. The adhesionbetween the graphene oxide and an electrical insulating resin is alsogood, and the adherence of the graphene oxide to a resin having a polargroup is particularly excellent.

In the transparent conductor of the present embodiment, when a stackincluding the metal nanowire layer 12, the graphene oxide layer 13, andthe insulating resin layer 14 is patterned, the transparent conductorcan be used for electric wiring. The electric wiring obtained bypatterning a transparent conductive film of the present embodiment hashigh transparency, and is excellent in resistance to bending, peeling,and impurities, is obtainable at low cost, and has low electricalresistance. Thus, a device having such an electric wiring has hightransparency and is excellent in resistance to bending, peeling, andimpurities. In addition, the device is advantageous also in that thedevice is low in electrical resistance and can be manufactured at lowcost.

In general, a metal wire having a diameter of about 10 to 500 nm and anaverage length of about 0.1 to 50 μm is referred to as a metal nanowire.The diameter of the metal nanowire can be measured by a scanningelectron microscope (SEM), for example. The average length of the metalnanowire can be determined by analyzing an SEM image, for example.

In the present embodiment, the diameter of the metal nanowire 12 a ispreferably 20 to 150 nm, and more preferably 30 to 120 nm. When theaverage length of the metal nanowire is too short, a sufficientconductive cluster is not formed, causing the electrical resistance tobecome high. Meanwhile, when the average length of the metal nanowire istoo long, the dispersion of the metal nanowire in a solvent during themanufacture of an electrode becomes unstable. The average length of themetal nanowire is preferably 1 to 100 μm, and more preferably 5 to 40μm.

The metal nanowire 12 a is preferably a silver nanowire. Silver has thesmallest electrical resistance, and is relatively stable even towardsoxygen or water. From the aspect of the price of the metal nanowire, acopper nanowire is also preferable. The metal nanowire may be made of analloy, and may have a surface subjected to plating using nickel or thelike.

The metal nanowire 12 a can be manufactured by reducing a metal ion inan aqueous solution using various reducing agents. By selecting the typeof the reducing agent, protective polymer, and coexisting ions usedduring manufacture, the shape and size of the metal nanowire can becontrolled. In order to manufacture the silver nanowire, it ispreferable that a polyhydric alcohol such as ethylene glycol is used asthe reducing agent, and polyvinylpyrrolidone is used as the protectivepolymer. Nano order sized wires, so-called nanowires, can be obtained byusing such raw materials.

The metal nanowire layer 12 can be formed by applying the dispersion ofthe metal nanowire 12 a in a liquid onto the transparent substrate 11. Amethod for applying the dispersion can be selected from a spin coatmethod, a spray coat method, an applicator coat method, or the like. Themetal nanowires may be fused to each other by a method such as heatingthe metal nanowire layer produced on the transparent substrate 11 at atemperature of 100° C. or more, or pressing the metal nanowire layer bya pressing machine. In such a case, the conductivity of the metalnanowire layer is further enhanced. A metal nanowire layer may beproduced by using metal nanowires having different diameters andmaterials. Thereby, sheet resistance, total light transmissivity, lightreflectivity, a Haze value, or the like can be changed.

The graphene oxide 13 a in the present embodiment is preferably planategraphene oxide obtained by oxidizing graphite. The graphene oxides 13 aare stacked to constitute the graphene oxide layer 13. When the numberof the graphene oxide layers is too small, resistance to impurities isnot sufficiently obtained. When the number of the graphene oxide layersis excessive, an increase in electrical resistance is of concern. Thenumber of the graphene oxide layers is preferably 2 to 100, and morepreferably 3 to 30.

The graphene oxide layer 13 can be formed by applying a dispersionobtained by dispersing graphene oxide in a polar solvent, followed bydrying. A basic compound, for example, ammonia, amines, sodiumhydroxide, or the like may be added into the polar solvent, if needed,in order to improve the dispersibility of the graphene oxide. Thegraphene oxide layer 13 may be a single layer or a multilayer including2 to 5 layers. When the diameter of the graphene oxide is too small, theresistance to impurities is insufficient. When the diameter of thegraphene oxide is excessive, the dispersibility of the graphene oxide inthe polar solvent is deteriorated, making it difficult to form anapplied film that is uniform. The diameter of the graphene oxide 13 a ispreferably 100 nm to 10 μm, and more preferably 300 nm to 4 μm.

The diameter of the plate-like graphene oxide is defined as a diameterof a circle having an area equal to the area of the plate. This diametercan be determined by analyzing an SEM image, for example.

When an oxygen content in the graphene oxide is too small, lightabsorption is increased, providing insufficient transparency. Meanwhile,when the oxygen content in the graphene oxide is excessive, there is aconcern that the barrier property against impurities may decrease. Theoxygen content in the graphene oxide is preferably 10 to 150% of thenumber of carbon atoms, and more preferably 30 to 120%.

The graphene oxide layer 13 may include metal nanoparticles within thegraphene oxide layer 13 or on the surface thereof. Contacts between thegraphene oxide 13 a and the metal nanowire 12 a and between the grapheneoxide layer 13 and the electric element are improved by including themetal nanoparticles. The metal nanoparticles are preferably made of thesame metal as that of the metal nanowire. When process conditions areproperly adjusted, the chemical reaction between the metal nanowire andthe graphene oxide allows the metal nanoparticles to be produced withoutseparately adding the metal nanoparticles.

When the diameter of the metal nanoparticle is too small, the stabilityof the nanoparticle is insufficient. When the diameter of the metalnanoparticle is excessive, an effect of a contact improvement cannot besufficiently obtained. When the metal nanoparticle having a largeparticle diameter is generated from the metal nanowire, the diameter ofthe metal nanowire serving as the raw material is decreased. In the caseof a transparent conductor in which the metal nanoparticle having alarge particle diameter is present, the transparent conductor is apt tobe short-circuited when applied to a touch panel. From theseconsiderations, the diameter of the metal nanoparticle is preferablyabout 1 to 50 nm, and more preferably 3 to 20 nm.

The electrical insulating resin layer 14 can be formed of athermoplastic, thermosetting or light, curing transparent resin. A resinhaving a polar group is preferably used, since then the adhesion betweenthe resin layer 14 and the graphene oxide layer 13 is enhanced.Particularly preferred is a resin having a carbonyl group, which islikely to bond with an —OH group of the graphene oxide through hydrogenbonding.

Among the resins described above, the thermoplastic resin or the lightcuring resin is particularly preferable. A production process using thethermoplastic resin is easy. The thermoplastic resin is particularlysuitable for applications requiring flexibility. For example, anacryl-based elastomer, a styrene-based elastomer, an olefin-basedelastomer, a vinyl chloride-based elastomer, a urethane-based elastomer,and an amide-based elastomer are used as the thermoplastic resin. Theacryl-based elastomer, urethane-based elastomer, and amide-basedelastomer, having a carbonyl group, are preferable.

The light curing resin is cured in a short time, enabling a process timefor device production to be shortened. Although the curing in a shorttime is apt to cause strain in the resin, layer, the metal nanowirelayer and the graphene oxide layer in the present embodiment areflexible, and can endure the strain. The graphene oxide functions alsoas a photopolymerization initiator for a vinyl monomer. As the lightcuring resin, a resin that is cured by ultraviolet light is preferable.Examples thereof include an acrylate radical polymerization-based resinand an epoxy cation polymerization-based resin. The acrylate-based resinis more preferable. After light irradiation, the light curing resin maybe subjected to a post-annealing treatment.

The material of the transparent substrate 11 can be selected from aresin and glass. However, from the aspects of flexibility and low cost,the material is preferably an electrical insulating resin. Examples ofthe resin include polyethylene terephthalate (PET), polyethylenenaphthalate (PEN), polycarbonate (PC), polyimide (PI), polyethersulphone (PES), a cyclic olefin resin (for example, ARTON or the like),and polymethylmethacrylate (PMMA). PET is the most preferableconsidering its particularly high mechanical strength and transparency,and its particularly low cost. The thickness of the transparentsubstrate 11 is preferably about 50 μm to 200 μm.

An antireflective film and a hard coat layer may be provided outside thesubstrate 11 made of PET. In order to form the antireflective film, forexample, an inorganic material such as MgF₂ and LiF, fluoride-basedpolymers, graphene oxide, or the like, which are low in refractive indexcan be used. In order to form the hard coat layer, an inorganic oxidesuch as SiO₂, a polyfunctional acrylic resin, or the like can be used,for example.

The hard coat layer is effective also as a barrier layer against oxygen,water vapor, or corrosive gases such as hydrogen sulfide. A binder layermay be provided on a surface of the hard coat layer that is in contactwith the metal nanowire 12 a in order to strengthen the bond between thehard coat layer and the metal nanowire 12 a. The binder layer can beformed by using polyvinyl alcohol, polyvinylpyrrolidone, graphene oxide,or the like, for example. Since interaction with the upper grapheneoxide layer becomes stronger, it is most preferable to use the grapheneoxide itself as the binder. In this case, the structure and oxygencontent of the graphene oxide used for the binder may be different fromthose of the graphene oxide of the graphene oxide layer 13. In order toenhance the adhesion between the binder layer and the PET film, theoxygen content of the graphene of the binder layer is preferably smallerthan that of the upper graphene oxide layer 13.

The graphene oxide layer 13 may include nitrogen atoms. The nitrogenatoms can be mixed into the graphene oxide layer 13 by adding a startingmaterial for the nitrogen atoms into a solvent dispersion that is theraw material for the graphene oxide layer 13. Examples of the startingmaterial include ammonia, amine compounds, hydrazine, and hydrazinecompounds. When the nitrogen atoms are present in the graphene oxidelayer, the binding between the graphene oxide layer and the metalnanowire is further strengthened.

When the graphene oxide layer 13 includes the nitrogen atoms in anamount of at least 0.1% of the carbon atoms, the effect of the nitrogenatoms can be obtained. The amount of the nitrogen atoms in the grapheneoxide layer 13 is more preferably 0.2% or more of the carbon atoms.Meanwhile, when the amount of the nitrogen atoms in the graphene oxidelayer 13 is excessive, there is a concern that the binding force betweenthe graphene oxides themselves may decrease. The amount of the nitrogenatoms is preferably 10% or less of the carbon. atoms, more preferably 6%or less, and most preferably about 0.2 to 4%.

The ratio (O/C) of the carbon atoms and oxygen atoms or the ratio (N/C)of the carbon atoms and nitrogen atoms can be measured by X-rayphotoelectron spectroscopy (XPS). The signal sensitivity variesdepending on the device. The signal strength of each element can beadjusted by using a material of known composition as a referencesubstance. An example of the standard substance of the ratio (N/C) ofthe carbon atoms and nitrogen atoms is carbon nitride, which has acomposition ratio of C₃N₄.

When the transparent conductor of the present embodiment is used forelectric wiring, the sheet resistance of a portion that becomes theelectric wiring is preferably 10 Ω/□ or less. If the sheet resistance isgreater than 10 Ω/□, when applying the electric wiring to an elementhaving a large area of A4 size (ISO 216) or more, there is a concernthat electrical resistance in the wiring may become great and therebyincreasing the drive voltage.

A part of the graphene oxide layer 13 is preferably present between themetal nanowire 12 a and the transparent substrate 11. In this case, thesame effect as that of the above-mentioned binder layer is obtained.Particularly, when the substrate 11 is made of a resin including anaromatic ring such as PET, PEN, and polycarbonate, the aromatic ring inthe resin interacts with the aromatic ring in the graphene oxide, andthereby the adhesion between the substrate 11 and the graphene oxidelayer 13 is enhanced. As a result, the adhesion between the metalnanowire 12 a and the substrate 11 is also improved.

FIG. 3 shows the configuration of a photoelectric conversion device,which includes a photoelectric conversion element, according to anembodiment. More specifically, a light-emitting device is shown as thephotoelectric conversion device, in which the photoelectric conversionelement is a light-emitting element. A light emitting device 30 shown inFIG. 3 includes a first support 33 having a light-transmission property,the first support 33 including a first transparent substrate 31 and afirst conductive layer 32 disposed on the first transparent substrate31; a second support 36 including a second substrate 34 and a secondconductive layer 35 disposed on the second substrate 34, the secondconductive layer 35 being spaced apart and faced to the first conductivelayer 32; a light-emitting element 37 including a semiconductor layer(an n-type semiconductor layer 37 b and a p-type semiconductor layer 37c), and a first electrode 37 a and a second electrode 37 d arranged onthe semiconductor layer, the light-emitting element 37 positionedbetween the first support 33 and the second support 36, wherein thefirst electrode 37 a is electrically connected to the first conductivelayer 32, and the second electrode 37 d is electrically connected to thesecond conductive layer 35; and an electrical insulating resin layer 38that is in contact with the first conductive layer 32 and the secondconductive layer 35. The first conductive layer 32 includes a metalnanowire layer including a plurality of metal nanowires and a grapheneoxide layer covering the metal nanowire layer.

In other words, in the light-emitting device 30, the light-emittingelement 37 is sandwiched between the first support 33 and the secondsupport 36, and the electrical insulating resin layer 38 is positionedin a region between the two supports and surrounding the light-emittingelement.

The first support 33 includes a first transparent substrate 31 and afirst conductive layer 32 disposed on the first transparent substrate31. The second support 36 includes a second substrate 34 and a secondconductive layer 35 disposed on the second substrate 34. The firstconductive layer 32 and the second conductive layer 35 are faced to eachother. The transparent substrate as already described is used as thefirst substrate 31. The transparent resin as already described is usedas the electrical insulating resin layer 38.

The first conductive layer 32 includes a metal nanowire layer includinga plurality of metal nanowires, and a graphene oxide layer covering themetal nanowire layer. It is preferable that the second substrate istransparent, and the second conductive layer 35 includes a metalnanowire layer including a plurality of metal nanowires and a grapheneoxide layer covering the metal nanowire layer.

The first conductive layer 32 and the second conductive layer 35 may bepatterned. The patterned first conductive layer 32 and second conductivelayer 35 can be arranged so that they cross each other.

The light-emitting element 37 is preferably an inorganic LED. Thelight-emitting element 37 includes an n-side electrode 37 a, an n-typesemiconductor layer 37 b, a p-type semiconductor layer 37 c, and ap-side electrode 37 d which are sequentially stacked. The n-sideelectrode 37 a in the light-emitting element 37 is electricallyconnected to the first conductive layer 32. The p-side electrode 37 d iselectrically connected to the second conductive layer 35. A conductiveadhesive layer may be provided between the n-side electrode 37 a and thefirst conductive layer 32, and between the p-side electrode 37 d and thesecond conductive layer 35. The antireflection layer and hard coat layerdescribed above are preferably provided on the surface of thelight-emitting device 30 (surfaces of the first substrate 31 and secondsubstrate 34). The circumference of the light-emitting device 30 ispreferably sealed to prevent the invasion of corrosive gas.

A photoelectric conversion device, which includes a photoelectricconversion element, according to another embodiment is shown in FIG. 4.More specifically, a light-emitting device is shown as the photoelectricconversion device, in which the photoelectric conversion element is alight-emitting element. A light-emitting device 40 shown in FIG. 4includes: a first support 43 having a light-transmission property, thefirst support 43 including a first transparent substrate 41 and asegmented conductive layer 42 disposed on the first transparentsubstrate 41; a second support 44 spaced apart from and faced to thesegmented conductive layer; a light-emitting element 45 including asemiconductor layer (an n-type semiconductor layer 45 b and a p-typesemiconductor layer 45 c), and a first electrode 45 a and a secondelectrode 45 d disposed on the semiconductor layer and spaced apart fromeach other, the light-emitting element 45 being positioned between thefirst support 43 and the second support 44, wherein the first electrode45 a and the second electrode 45 d are electrically connected todifferent segments of the segmented conductive layer 42; and anelectrical insulating resin layer 46 that is in contact with thesegmented conductive layer 42 and the second support 44. The segmentedconductive layer 42 includes a metal nanowire layer including aplurality of metal nanowires and a graphene oxide layer covering themetal nanowire layer.

In other words, in the light-emitting device 40, the light-emittingelement 45 is sandwiched between the first support 43 including thefirst substrate 41 and the second support 44. The light-emitting element45 is embedded in the electrical insulating resin layer 46. The firstsupport 43 includes the segmented conductive layer 42 disposed on thefirst substrate 41. The segmented conductive layer 42 is faced to thesecond support 44. The transparent substrate as already described isused as the first substrate 41. The transparent resin as alreadydescribed is used as the electrical insulating resin layer 46.

The segmented conductive layer 42 includes a metal nanowire layerincluding a plurality of metal nanowires and a graphene oxide layercovering the metal nanowire layer. The segmented conductive layer 42 hasa spacing 42 a. An electrical insulating resin is positioned in thespacing 42 a.

The light-emitting element 45 is preferably an inorganic LED. Thelight-emitting element 45 includes a p-type semiconductor layer 45 c andan n-type semiconductor layer 45 b covering a part of the p-typesemiconductor layer 45 c. An n-side electrode 45 a is disposed on then-type semiconductor layer 45 b. A p-side electrode 45 d is disposed onthe p-type semiconductor layer 45 c which is not covered with the n-typesemiconductor layer 45 b. The n-side electrodes 45 a and the p-sideelectrode 45 d are electrically connected to different segments of thesegmented conductive layer 42. A conductive adhesive layer may beprovided between the n-side electrode 45 a and the segmented conductivelayer 42, and between the p-side electrode 45 d and the segmentedconductive layer 42. The n-side electrode 45 a and the p-side electrode45 d are electrically insulated by the electrical insulating resinpositioned in the spacing 42 a of the segmented conductive layer 42. Theantireflection layer and hard coat layer described above are preferablyprovided on the surface of the light-emitting device 40 (surfaces of thefirst substrate 41 and the second support 44). The circumference of thelight-emitting device 40 is preferably sealed to prevent the invasion ofcorrosive gas.

With reference to FIGS. 5A to 5C, 6A and 6B, a coordinate panelaccording to another embodiment will be described. FIG. 5A describes theconfiguration of the plane of the coordinate panel. FIGS. 5B and 5C arerespectively plan views of a first wiring board and second wiring board.FIGS. 6A and 6B show cross-sectional views of the coordinate panel. FIG.6A is a cross-sectional view taken along A-A′ in FIG. 5A. FIG. 6B is across-sectional view taken along B-B′ in FIG. 5A.

A coordinate panel 50 shown in FIGS. 5A to 5C, 6A and 6B includes: afirst wiring board 57 including a first transparent substrate 51 and afirst conductive layer 52 disposed on the first transparent substrate51, the first conductor layer 52 being patterned to extend in a firstdirection; a second wiring board 58 including a second transparentsubstrate 53 and a second conductive layer 54 disposed on the secondtransparent substrate 53, the second conductive layer 54 being spacedapart from and faced to the patterned first conductive layer, andpatterned to extend in a second direction crossing the first direction;and an electrical insulating resin layer 56 that is in contact with thefirst substrate 51, the first conductive layer 52, the secondtransparent substrate 53, and the second conductive layer 54. Each ofthe first conductive layer 52 and the second conductive layer 54includes a metal nanowire layer including a plurality of metal nanowiresand a graphene oxide layer covering the metal nanowire layer.

As shown in the plan view of FIG. 5A to 5C, the coordinate panelincludes an x electrode 52 extending in an x direction and a y electrode54 extending in a y direction crossing the x direction. A pad 55consists of parts 52′ of an x wiring 52 and parts 54′ of a y wiring 54as shown in FIGS. 6A and 6B.

The first wiring board 57 includes the first transparent substrate 51and the plurality of x wirings 52 disposed on the first transparentsubstrate 51. The second wiring board 58 includes the second transparentsubstrate 53 and the plurality of y wirings 54 disposed on the secondtransparent substrate 53. The x wiring 52 and the y wiring 54 areseparated by the electrical insulating resin layer 56. The transparentsubstrate as already described is used as the first substrate 51 and thesecond substrate 53. The transparent resin as already described is usedfor the electrical insulating resin layer 56.

The x wiring 52 and the y wiring 54 include a metal nanowire layerincluding a plurality of metal nanowires and a graphene oxide layercovering the metal nanowire layer. The x wiring 52 and the y wiring 54can be said to be patterned conductive layers. The antireflection layerand hard coat layer described above are preferably provided on thesurface of the coordinate panel 50 (surfaces of the first base substrate51 and second base substrate 53). The circumference of the coordinatepanel 50 is preferably sealed to prevent the invasion of corrosive gas.

The coordinate panel of the present embodiment is suitable as anelectrostatic capacitive touch panel. A thermoplastic or curing resincan be used in order to form the electrical insulating resin layer.

Hereinafter, specific examples of each embodiment will he shown.

EXAMPLE 1

A light-emitting device 30 shown in FIG. 3 is produced by the followingmethod.

A surface of a PET film, as the first substrate, is made slightlyhydrophilic by a UV ozone treatment. Silver nanowires (average diameter:40 nm, length: 20 to 80 μm) manufactured by Nano Meet, as the metalnanowires, are dispersed in methanol to prepare a 0.2 mg/ml methanoldispersion. The obtained dispersion is applied by a spray method througha mask onto the PET film held at 80° C. to obtain a wiring pattern.Furthermore, this is dried at 60° C. for 10 minutes to produce a silvernanowire layer. The sheet resistance of the silver nanowire layermeasured by a four Probe method is about 10 Ω/□.

An ethanol dispersion of graphene oxide is applied onto the silvernanowire layer. The graphene oxide has a particle diameter of 500 nm to3 μm, is produced from graphite, and has a ratio (O/C) of oxygen atomsto carbon atoms of 120%. About ten layers of the ethanol dispersion ofgraphene oxide are applied onto the entire silver nanowire layer anddried at 60° C. for 10 minutes to obtain a graphene oxide layer. Thesheet resistance of a complex including the metal nanowire layer and thegraphene oxide layer is decreased to about 7 Ω/□ by this procedure.

The number of the graphene oxide layers can be determined as follows.The graphene oxide is reduced by hydrazine to convert the graphene oxideinto graphene. When the graphene layer is irradiated with light of 550nm, 2.3% of the light is absorbed per graphene layer. The number of thegraphene oxide layers is determined by comparing the absorption amountof light at 550 nm between the graphene oxide layer and graphene layer.This method is a destructive inspection since the graphene oxide layeris converted into a graphene layer.

The complex formed on the PET film as described above serves as a lowerelectrode. An upper electrode is separately formed on a PET film by thesame procedure as described above.

SEM images of the obtained complex are shown in FIGS. 7A and 7B. FIG. 7Ashows a surface SEM image. FIG. 7B shows a cross-sectional SEM image. Asshown in FIG. 7A, a plurality of silver nanowires 12 a are covered witha graphene oxide layer 13. Silver nanoparticles 16 having diameters ofabout 10 nm is present on one surface. The cross-sectional SEM image ofFIG. 7B shows that the silver nanowires 12 a are three-dimensionallystacked. The graphene oxide layer cannot be distinguished in thecross-sectional SEM image. In addition, since silver nanoparticles arenot observed, most of the silver nanoparticles are considered to bepresent on the outermost surface of the graphene oxide layer.

The Pt—Pd layer shown in FIG. 7B has been separately vapor-deposited inorder to distinguish the outermost surface. The re-deposition layer isone that has formed due to the re-adhesion of sample material sputteredby an ion beam while producing the sample cross-section. Although theimage is not clear, a slight gap is observed at the interface betweenthe silver nanowire layer 12, which includes a plurality of silvernanowires 12 a, and the Pt—Pd layer. Graphene oxide layer is consideredto be present also in the gap.

By providing the graphene oxide layer on the silver nanowire layer, thehydrophilicity of the surface is increased, thereby increasing thespread area of water by about 50%. Furthermore, resistance to sulfurvapor is also enhanced. When the graphene oxide layer is not provided,leaving the silver nanowire layer for 15 minutes at 80° C. in thepresence of sulfur vapor results in the sheet resistance of the silvernanowire layer to significantly increase by 10⁶ Ω/□ or more. Meanwhile,when the graphene oxide layer is provided, the sheet resistance of thesilver nanowire layer increases only by about 10² Ω/□, even if thesilver nanowire layer is left at 80° C. for 15 minutes.

A red LED chip having a pair of electrodes on its top and bottom sidesis prepared as a light-emitting element. The LED chip is pressed ontothe lower electrode. An acrylic ultraviolet curing resin is applied ontothe entire lower electrode having the LED chip to form an electricalinsulating resin layer. The upper part of the LED chip is washed with anorganic solvent.

A PET film having an upper wiring is laminated onto the LED chip so thatthe upper wiring and a lower wiring cross each other at the position ofthe LED chip, and then the entire laminate stack is irradiated withultraviolet light. Then, the light emitting device of the presentexample is obtained by most-annealing at 60° C.

The light-emitting device of the present example exhibits bright lightemission observed under conditions of a direct current of 15 to 20 mA at2.0 V, and has high transparency. The light-emitting device of thepresent example is excellent in resistance to repetitive bending,peeling, and impurities. In addition, the light-emitting device is lowin electrical resistance as described above, and can be produced at lowcost.

EXAMPLE 2

A light-emitting device 40 shown in FIG. 4 is produced by the followingmethod.

A surface of a PET film, as the first substrate, is made slightlyhydrophilic by a UV ozone treatment. Furthermore, a polyvinylalcohol-based hydrophilic binder resin is applied to form a binderlayer. A 2 mg/ml ethanol dispersion of silver nanowires (averagediameter: 35 nm, average length: 15 μm) manufactured by Blue Nano isapplied onto the binder layer by a bar coater. This is dried at 60° C.for 10 minutes to produce a silver nanowire layer.

About 20 layers of the same ethanol dispersion of graphene oxide as thatin Example 1 are applied onto the entire silver nanowire layer and driedat 60° C. for 10 minutes to obtain a graphene oxide layer. The silvernanowire layer and the graphene oxide layer are stacked to form aconductive layer. This conductive layer is patterned by an yttriumaluminum garnet laser (NAG laser) to obtain a wiring.

A blue LED chip having a pair of electrodes on one surface is preparedas a light-emitting element. The LED chip is pressed and placed on thewiring obtained above. An acrylic ultraviolet curing resin is appliedonto the entire wiring having the LED chip to form an electricalinsulating resin layer. A PET film, as the second support, is laminatedon the electrical insulating resin layer, and then the entire laminatestack is irradiated with ultraviolet light. Finally, the light-emittingdevice of the present example is obtained by post-annealing at 60° C.

The light-emitting device of the present example exhibits bright lightemission observed under conditions of a direct current of 15 to 20 mA at3.7 V, and has high transparency. The light-emitting device of thepresent example is low in electrical resistance, and excellent inresistance to repetitive bending, peeling, and impurities. Thelight-emitting device can be produced at low cost.

EXAMPLE 3

A light-emitting device 40 shown in FIG. 4 is produced by the followingmethod.

About ten layers of the same ethanol dispersion of graphene oxide asthat in Example 1 are applied onto an entire surface of a PET film, asthe first substrate, and dried at 60° C. for 10 minutes. Thereby, alower graphene oxide layer is obtained as a binder layer. Silvernanowires (average diameter: 40 nm) manufactured by Nano Meet, as themetal nanowires, are dispersed in methanol to prepare a 2 mg/ml methanoldispersion. The obtained dispersion is applied onto the lower grapheneoxide layer by a bar coater. This is dried at 60° C. for 10 minutes toproduce a silver nanowire layer.

As a raw material for an upper graphene oxide layer, there is preparedan aqueous dispersion of graphene oxide, the graphene oxide beingproduced from graphite and having a ratio (O/C) of oxygen atoms tocarbon atoms of 37% and a particle diameter of 300 nm to 1 μm(containing 0.4% by weight of ammonia). About ten layers of the aqueousdispersion are applied onto the entire silver nanowire layer and driedat 90° C. for 20 minutes to obtain the upper graphene oxide layer. AnN/C atom ratio determined from XPS is 3 to 4%. The lower graphene oxidelayer, the silver nanowire layer, and the upper graphene oxide layer arestacked to obtain a conductive layer. This conductive layer is patternedby a YAG laser to obtain a wiring.

A blue LED chip having a pair of electrodes on one surface is preparedas a light-emitting element. The LED chip is pressed and placed on thewiring obtained above. An acrylic ultraviolet curing resin is appliedonto the entire wiring having the LED chip to form an electricalinsulating resin layer. A PET film, as the second support, is laminatedon the electrical insulating resin layer, and then the entire laminatestack is irradiated with ultraviolet light. Finally, the light-emittingdevice of the present example is obtained by post-annealing at 60° C.

The light-emitting device of the present example exhibits bright lightemission observed under conditions of a direct current of 15 to 20 mA at3.6 V, and has high transparency. The light-emitting device of thepresent example is low in electrical resistance, and excellent inresistance to repetitive bending, peeling, and impurities. Thelight-emitting device can be produced at low cost.

EXAMPLE 4

A coordinate panel 50 shown in FIG. 5A is produced by the followingmethod.

A surface of a PET film, as the first substrate, is made slightlyhydrophilic by a UV ozone treatment. Furthermore, a polyvinylalcohol-based hydrophilic binder resin is applied onto the surface ofthe PET film to form a binder layer. Silver nanowires (average diameter:40 nm) manufactured by Nano Meet, as the metal nanowire, are dispersedin methanol to prepare a 2 mg/ml methanol dispersion. The obtaineddispersion is applied onto the binder layer by a bar coater. This isdried at 60° C. for 10 minutes to produce a silver nanowire layer.

About 20 layers of the same ethanol dispersion of graphene oxide as thatin Example 1 are applied onto the entire silver nanowire layer and driedat 60° C. for 10 minutes to obtain a graphene oxide layer. The silvernanowire layer and the graphene oxide layer are stacked to form aconductive layer. This conductive layer is patterned by a YAG laser toform an x wiring and a pad in the x wiring, thereby obtaining a firstwiring board. A conductive, layer is formed on a PET film by the sameprocedure as described above, and processed by a YAG laser. Thus, a ywiring and a pad in the y wiring are formed to obtain a second wiringsubstrate.

An acrylic ultraviolet curing resin is applied onto the entire PET film(first wiring board) on which the x wiring is produced, to form anelectrical insulating resin layer. The PET film (second wiring board) onwhich the y wiring is formed is laminated on the electrical insulatingresin layer so that the pads are shifted from each other, and the entirelaminate stack is irradiated with ultraviolet light. Then, thecoordinate panel used for a capacitive touch panel is obtained bypost-annealing at 60° C.

The coordinate panel of the present example is excellent in resistanceto repetitive bending, peeling, and impurities. The coordinate panel canbe produced at low cost.

EXAMPLE 5

A light-emitting device 30 shown in FIG. 3 is produced by the followingmethod.

A silver nanowire layer and a graphene oxide layer are produced on thesurface of a PET film, as the first substrate, in the same manner as inExample 1. Next, the graphene oxide layer is brought into contact withhydrazine hydrate vapor for 10 minutes at 90° C. Therefore, a part ofgraphene oxide is reduced, and nitrogen atoms are introduced. An N/Catom ratio determined, from XPS is 0.3 to 0.5%.

A complex formed on the PET film as described above serves as a lowerelectrode. An upper electrode is separately formed on a PET film by thesame procedure as described above.

A red LED chip having a pair of electrodes on its top and bottom sidesis prepared as a light-emitting element. The LED chip is pressed andplaced on the lower electrode. An acrylic ultraviolet curing resin isapplied onto the entire lower electrode having the LED chip to form anelectrical insulating resin layer. The upper part of the LED chip iswashed with an organic solvent.

A PET film having an upper wiring is laminated onto the LED chip so thatthe upper wiring and a lower wiring cross each other at the position ofthe LED chip, and then the entire laminate stack is irradiated withultraviolet light. Then, the light-emitting device of the presentexample is obtained by post-annealing at 60° C.

The light-emitting device of the present example exhibits bright lightemission observed under conditions of a direct current of 15 to 20 mA at2.0 V, and has high transparency. The light-emitting device of thepresent example is excellent in resistance to repetitive bending,peeling, and impurities. In addition, the light-emitting device is lowin electrical resistance as described above, and can be produced at lowcost.

EXAMPLE 6

A light-emitting device 40 shown in FIG. 4 is produced by the followingmethod.

Graphene oxide having a particle diameter of 200 to 500 nm and an O/Catom ratio of 57% is used as the granhene oxide. A 1 mg/ml methanoldispersion of silver nanowires (average diameter 110 nm, average length:30 μm) manufactured by Seashell Technology is used. In all otherrespects, a light-emitting device is produced in the same manner as inExample 2.

The light-emitting device of the present example exhibits bright lightemission observed under conditions of a direct current of 15 to 20 mA at2.0 V, and has high transparency. The light-emitting device of thepresent example is excellent in resistance to repetitive bending,peeling, and impurities. In addition, the light-emitting device is lowin electrical resistance as described above, and can be produced at lowcost.

EXAMPLE 7

A light-emitting device 40 shown in FIG. 4 is produced by the followingmethod.

A surface of a PET film, as the first substrate, is made slightlyhydrophilic by a UV ozone treatment. Furthermore, a polyvinylalcohol-based hydrophilic binder resin is applied to the surface of thePET film to form a binder layer. A 2 mg/ml ethanol dispersion of silvernanowires (average diameter: 35 nm, average length: 15 μm) manufacturedby Blue Nano is applied onto the binder layer by a bar coater. This isdried at 60° C. for 10 minutes to produce a silver nanowire layer.

About 20 layers of the same ethanol dispersion of graphene oxide as thatin Example 1 are applied onto the entire silver nanowire layer and driedat 60° C. for 10 minutes to obtain a graphene oxide layer. The silvernanowire layer and the graphene oxide layer are stacked to form aconductive layer. This conductive layer is patterned by a YAG laser toobtain a wiring.

A thermoplastic acrylic elastomer film is prepared. A through-holecorresponding to an LED chip is opened in the thermoplastic acrylicelastomer film. The acrylic elastomer film is adhered on a conductivelayer so that the through-hole is positioned on a pair of wiringelectrodes. A blue LED chip having a pair of electrodes on one surfaceis prepared as a light-emitting element. The LED chip is pressed intothe through-hole obtained above, and placed on the pair of wirings. APET film, as the second support, is laminated thereon, followed byheating, thereby obtaining the light-emitting device of the presentexample.

The light-emitting device of the present example exhibits bright lightemission observed under conditions of a direct current of 15 to 20 mA at3.7 V, and has high transparency. The light-emitting device of thepresent example is low in electrical resistance, and is excellent inresistance to repetitive bending, peeling, and impurities. Thelight-emitting device can be produced at low cost.

According to the embodiments described above, a transparent conductorthat is low in electrical resistance is provided, in which thetransparent conductor has high transparency, is excellent in resistanceto bending, peeling, and impurities, and is obtainable at low cost, thetransparent conductor comprising: a transparent substrate; a metalnanowire layer disposed on the transparent substrate and comprising aplurality of metal nanowires; a graphene oxide layer covering the metalnanowire layer; and an electrical insulating resin layer disposed incontact with the graphene oxide layer.

While certain embodiments have been described, these embodiments havebeen presented by way of example only, and are not intended to limit thescope of the inventions. Indeed, the novel, methods and systemsdescribed herein may be embodied in a variety of other forms;furthermore, various omissions, substitutions and changes in the form ofthe methods and systems described herein may be made without departingfrom the spirit of the inventions. The accompanying claims and theirequivalents are intended to cover such forms or modifications as wouldfall within the scope and spirit of the inventions.

What is claimed is:
 1. A transparent conductor comprising: a transparentsubstrate; a metal nanowire layer disposed on the transparent substrateand comprising a plurality of metal nanowires; a graphene oxide layercovering the metal nanowire layer; and an electrical insulating resinlayer disposed in contact with the graphene oxide layer.
 2. Thetransparent conductor according to claim 1, wherein a stack comprisingthe metal nanowire layer, the graphene oxide layer, and the electricalinsulating resin layer is patterned.
 3. The transparent conductoraccording to claim 1, wherein the graphene oxide layer comprises metalnanoparticles therein or thereon.
 4. The transparent conductor accordingto claim 1, wherein the metal nanowires are silver nanowires.
 5. Thetransparent conductor according to claim 1, wherein the electricalinsulating resin layer comprises a resin having a polar group.
 6. Thetransparent conductor according to claim 1, further comprising thegraphene oxide layer interposed between the transparent substrate andthe metal nanowire layer.
 7. A coordinate panel comprising: a firstwiring board comprising a first transparent substrate and a firstconductive layer disposed on the first transparent substrate, the firstconductive layer being patterned to extend in a first direction; asecond wiring board comprising a second transparent substrate and asecond conductive layer disposed on the second transparent substrate,the second conductive layer being spaced apart from and faced to thepatterned first conductive layer, and patterned to extend in a seconddirection crossing the first direction; and an electrical insulatingresin layer that is in contact with the first transparent substrate, thefirst conductive layer, the second transparent substrate, and the secondconductive layer, wherein each of the first and second conductive layerscomprises a metal nanowire layer comprising a plurality of metalnanowires and a graphene oxide layer covering the metal nanowire layer.8. A photoelectric conversion device comprising: a first support havinga light-transmission property, the first support comprising a firsttransparent substrate and a first conductive layer disposed on the firsttransparent substrate; a second support comprising a second transparentsubstrate and a second conductive layer disposed on the secondtransparent substrate, the second conductive layer being spaced apartfrom and faced to the first conductive layer; a photoelectric conversionelement comprising a semiconductor layer, and first and secondelectrodes arranged on the semiconductor layer, the light-emittingelement being positioned between the first support and the secondsupport, wherein the first electrode is electrically connected to thefirst conductive layer, and the second electrode is electricallyconnected to the second conductive layer; and an electrical insulatingresin layer that is in contact with the first conductive layer and thesecond conductive layer, wherein the first conductive layer comprises ametal nanowire layer comprising a plurality of metal nanowires and agraphene oxide layer covering the metal nanowire layer.
 9. Aphotoelectric conversion device comprising: a first support having alight-transmission property, the first support comprising a firsttransparent substrate and a segmented conductive layer disposed on thefirst transparent substrate; a second support spaced apart from andfaced to the segmented conductive layer; a photoelectric conversionelement comprising a semiconductor layer, and first and secondelectrodes disposed on the semiconductor layer and spaced apart fromeach other, the light-emitting element being positioned between thefirst support and the second support, wherein the first electrode andthe second electrode are electrically connected to different segments ofthe segmented conductive layer; and an electrical insulating resin layerthat is in contact with the segmented conductive layer and the secondsupport, wherein the segmented conductive layer comprises a metalnanowire layer comprising a plurality of metal nanowires and a grapheneoxide layer covering the metal nanowire layer.
 10. The photoelectricconversion device according to claim 8, wherein the photoelectricconversion element is a light-emitting element.
 11. The photoelectricconversion device according to claim 9, wherein the photoelectricconversion element is a light-emitting element.
 12. The photoelectricconversion device according to claim 10, wherein the photoelectricconversion device is an inorganic light-emitting diode.
 13. Thephotoelectric conversion device according to claim 11, wherein thephotoelectric conversion device is an inorganic light-emitting diode.